Think of N2 as nitrogen gas purity. When a minimum percentage is specified, it means the gas must be at least that pure to be considered nitrogen for the intended use, such as creating an inert or blanketing atmosphere. If you only had 60% N2, the remaining 40% would bring in enough other gases (often including oxygen) to compromise the inert conditions. The options that imply more than 100% nitrogen aren’t physically possible, and ranges that are too low wouldn’t meet the standard for an effective inert environment. Therefore, the minimum acceptable nitrogen content is 95%.

Oil pressure must stay above a minimum level to ensure oil keeps flowing to all moving parts for proper lubrication. When the engine is hot and running at normal speeds, you expect the pressure to be above this floor; it can be higher when the engine is cold or at higher RPM. The specified minimum around 40 psi serves as that floor to prevent excessive wear. If the pressure drops to zero or very low (like 0 psi), that signals a serious problem with the oil pump, pickup, leaks, or viscosity, and the engine could be damaged. Pressures like 80 psi or 110 psi are typical during higher RPM or cold conditions, not the minimum acceptable value. Therefore, 40 psi is the correct minimum.

As x grows without bound, arctan x approaches π/2. The arctan function gives the angle whose tangent is x, and its outputs lie in the interval (-π/2, π/2). As the tangent value x becomes arbitrarily large, the corresponding angle must get arbitrarily close to the vertical ray, i.e., π/2, from below. Tangent blows up near π/2, so you can make the angle as close to π/2 as you like, but never actually reach it for any finite x. Hence the limit is π/2.

N1 transient limits define how much the engine speed can briefly overshoot the normal maximum during fast throttle changes, and for how long that overspeed can be held. This reflects a balance: a short, controlled spike is tolerable because engines experience brief surges, but staying above the limit too long or by too much risks stressing components. The specified transient limit of 103.8% for 30 seconds means N1 may peak at 103.8% for up to half a minute during transient conditions, then must settle back down. This combination protects turbine blades and other hardware while still allowing responsive throttle movement. The other options don’t fit typical transient limits: 60% for 60 seconds would be far too low to allow normal transient behavior; 101–103% for 2 minutes would exceed safe duration for a near-limit overspeed; 103.2% for 5 minutes would also be unsafe due to both the higher-than-desired overshoot and the much longer duration.